Gear pump with internal rotors are being used more and more as oil pumps and for filling gearboxes or other pumps, on the one hand, and to lubricate internal combustion engine, on the other hand. In all cases, the requirements, in part, consist of producing the most uniform possible pulse-free delivered stream, minimizing the effects of cavitation in the pump, and reducing the noise accompanying cavitation and pulsation. This invention is intended to improve gear pumps with internal rotors for oil delivery in line with these requirements.
The oil to be delivered is fed to known pumps through a suction channel running in the pump housing as tangentially as possible essentially at the meshing point of the gears between inner and outer rotors in a reniform suction chamber, also know as a reniform suction element transported between the teeth of the two rotor, and fed out of the housing through a pressure channel as tangentially as possible to the points of use by a reniform pressure chamber, also know, as a reniform pressure element. In the known designs, the suction and pressure channels are located only on one side, usually for space reasons of the housing side of the pair of gears, while the side of the housing ending in the transport chamber, usually the cover, has a smooth surface on the inside of the pump. The stream of oil thus enters the transport chamber at one side of the pair of gear rotors and leaves it on the same side. Such a pump is described, for example, in DE-PS 3410015 or EP-PS 0161421. Gear pumps for oil with internal rotors of the type described often reach a state of cavitation at high speeds. Since the transport chambers between the teeth of the pair of rotors are no longer completely filled at very high rotational speeds, air is dissolved in the transported oil at reduced pressure and oil vapor is formed. The gases implode with increasing pressure on the pressure side, with the noise level, the pressure pulsation, and the power consumption rising. In particularly negative cases, pump parts may be mechanically attacked by these implosions and even destroyed. Attempts to obviate these incidents in the past have been limited to changing the contours, particularly those of the reniform infeed channel, i.e., to lengthen or shorten it, anal also, for example, to split it into two sub-kidneys at its end. However, the result of these efforts so far has not been satisfactory. Benefits achieved produced drawbacks elsewhere.
The invention modifies the spaces available in the pump for suction and pressure by placing additional reniform chambers at the side opposite the inflow and outflow, usually in the cover, which essentially correspond to the reniform suction and pressure chambers but differ from them in part, particularly in their radial extent.
Such designs are likewise already known in principle to the extent of additional opposing reniform chambers being positioned opposite the inflow and outflow side, for example from DE OS 2 249 395, DE PS 35 06 920 C2, or DE OS 29 34 002 A1. All of the designs of this type disclosed so far, however, pursue the objective only of bringing the fluid to be transported also to the opposite side of the pair of rotors in order to have the lateral pressure which is acting the pair of rotors, act on both sides and thus to prevent the rotors from running into a wall of the housing with the resultant harmful consequences on power and pump wear. Thus, the problem focused an in these prior publications is not to improve the filling of cavities between the teeth and to reduce cavitation by different reniform chambers designs on the inflow/outflow side on the one hand and the opposite side on the other. In the same way, there are no differing reniform chambers designs deduced from them.